1. Field of the Invention
The present invention relates to a fluid-filled elastic cylindrical mount or bushing which is suitably usable as an automobile engine mount or suspension bushing and which exhibits a desired vibration damping effect based on flow of a fluid therethrough.
2. Discussion of the Related Art
As one type of a vibration damping elastic bushing or mount interposed between two members of a vibration system, there is known a fluid-filled elastic cylindrical mount as disclosed in JP-A-56-164242, comprising: a generally cylindrical core portion including a center shaft member fixed to one of the two members of the vibration system, an intermediate sleeve disposed radially outwardly of the center shaft member with a predetermined radial spacing therebetween, and an elastic body interposed between and connecting the center shaft member and the intermediate sleeve, the core portion having at least one pocket open in the outer circumferential surface thereof; and an outer sleeve portion fixed to the other of the two members of the vibration system and having a cylindrical bore in which the core portion is fixedly received, whereby the center shaft member and the outer sleeve portion are elastically connected to each other by the elastic body, and the at least one pocket is closed by the outer sleeve portion to provide at least one fluid chamber filled with a non-compressible fluid. The elastic cylindrical mount constructed as described above can be readily adapted to be capable of exhibiting an excellent vibration damping effect based on resonance or flows of the non-compressible fluid therethrough, which effect would not be obtained from the elasticity of the elastic body alone, in the absence of the fluid. Thus, the fluid-filled elastic cylindrical mount has been widely used as an engine mount or suspension bushing for automotive vehicles.
Such fluid-filled elastic cylindrical mounts are required to have a sufficient degree of fluid tightness to prevent leakage of the non-compressible fluid from the fluid chamber. To this end, a sealing member is interposed between the intermediate sleeve of the core portion and the outer sleeve portion, and is squeezed by and between the intermediate sleeve and the outer sleeve portion.
In assembling the mount, the core portion is press-fitted in the bore of the outer sleeve portion. The sealing member interposed between the intermediate sleeve and the outer sleeve portion tends to be damaged due to a force applied thereto upon press-fitting of the core portion in the outer sleeve portion. Accordingly, the conventional mount suffers from difficulty in securing high stability in its fluid tightness. Where the outer sleeve portion is an outer sleeve formed of a metallic material, the mount may be assembled by drawing the metallic outer sleeve radially inwards onto the outer circumferential surface of the core portion. However, the drawing operation requires an expensive device, and is cumbersome or difficult to perform, resulting in an undesirably high cost of manufacture of the mount.
It is considered possible to use a split outer sleeve portion consisting of a plurality of part-cylindrical sections. When the cylindrical mount is assembled, these part-cylindrical sections are placed on the outer circumferential surface of the core portion and are butted together at abutting end faces thereof along straight lines substantially parallel to the axis of the mount, so that the sections are arranged in the circumferential direction of the mount. The part-cylindrical sections are fixed to each other by bonding, welding, fastening or any other suitable means. This method permits simultaneous formation and fluid-tight assembling of the outer sleeve portion on the core portion, while preventing damage of the sealing member during the assembling, and eliminating an expensive device such as a drawing device, whereby the production efficiency of the mount is significantly improved.
A further study by the present inventor of the fluid-filled elastic cylindrical mount using the outer sleeve portion consisting of a plurality of part-cylindrical sections has revealed difficulty to fix the part-cylindrical sections to each other at their circumferential ends while assuring a high degree of fluid tightness at the abutting end faces. Thus, this mount has a potential problem of difficulty in obtaining high stability in its performance and operating reliability.